Abstract
Purpose To compare two calculators for toric intraocular lens (IOL) calculation and to evaluate the prediction of refractive outcome. Methods Sixty-four eyes of forty-five patients underwent cataract surgery followed by implantation of a toric intraocular lens (Zeiss Torbi 709 M) calculated by a standard industry calculator using front keratometry values. Prediction error, median absolute error, and refractive astigmatism error were evaluated for the standard calculator. The predicted postoperative refraction and toric lens power values were evaluated and compared after postoperative recalculation using the Barrett calculator. Results We observed a significant undercorrection in the spherical equivalent (0.19 D) by using a standard calculator (p ≤ 0.05). According to the Baylor nomogram and the refractive influence of posterior corneal astigmatism (PCA), undercorrection of the cylinder was lower for patients with WTR astigmatism, because of the tendency of overcorrection. An advantage of less residual postoperative SE, sphere, and cylinder for the Barrett calculator was observed when retrospectively comparing the calculated predicted postoperative refraction between calculators (p ≤ 0.01). Conclusion Consideration of only corneal front keratometric values for toric lens calculation may lead to postoperative undercorrection of astigmatism. The prediction of postoperative refractive outcome can be improved by using appropriate methods of adjustment in order to take PCA into account.
Highlights
During the last few years, the demand of patients undergoing cataract surgery for age-related cataract has increased
Adjustment of standard industry-based calculators by a new regression formula to calculate the total corneal astigmatism (TCA) can improve the error in predicted postoperative astigmatism [11]
IOLMaster 500 (Zeiss Meditec, Oberkochen, Germany) was used and preoperative Scheimpflug measurement for total corneal astigmatism assessment was carried out in all patients. These patients underwent coaxial microincision high fluidic cataract surgery (CoMICS) and phacoemulsification (Oertli OS3 device, Oertli, Switzerland) by an experienced surgeon (A.K.) who carried out a clear corneal incision (CCI) at 90° with an estimated surgeon-specific surgically induced astigmatism of ≤0.5 D followed by implantation of a toric intraocular lens (Zeiss Torbi 709 M) calculated by a standard industry-based calculator (ZCalc, Zeiss Meditec, Oberkochen, Germany)
Summary
During the last few years, the demand of patients undergoing cataract surgery for age-related cataract has increased. A higher error in refractive astigmatism (ERA) has been shown to be obtained by ignoring the posterior corneal astigmatism (PCA) in toric lens calculation [7]. The most commonly used biometers (manual and IOLMaster 500) rely purely on measurements of the anterior curvature when measuring corneal astigmatism. This may lead to poor prediction of the total corneal astigmatism (TCA). By using nomograms such as the Baylor nomogram or the Barrett calculator, PCA can be predicted dependent on the power and axis of the ACA [8, 9]. Adjustment of standard industry-based calculators by a new regression formula to calculate the TCA can improve the error in predicted postoperative astigmatism [11]
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